The present invention relates to custom packaging of fragile articles. There are several basic ways to protect such articles, particularly when they are to be stored or shipped in generally rectangular containers such as cardboard boxes. One method is to fill the areas surrounding the fragile object in the box with a loose friable material such as expanded polystyrene pieces, shredded paper, or popcorn. Although providing an appropriate cushion, such packaging techniques generally require large amounts of storage space for the friable material before it is used, and tend to produce large amounts of unwanted loose material when the packages are opened.
A second method is to form a custom rigid framework, typically of polystyrene foam, that positions and maintains a particular object in place in a particular sized box. Although this can be useful and efficient where large numbers of identical items are repeatedly placed in identical boxes, it lacks the flexibility required in some packaging operations in which the sizes and shapes of the objects being packaged may constantly vary. For example, a number of packagers supply a wide variety of items of different sizes and shapes to their customers on a regular basis.
A third form of custom packaging is foam-in-place packaging. In such applications, the fragile article is typically placed into a container such as a cardboard box and covered with a plastic sheet material after which a mixture of polymer precursor chemicals is injected into the empty spaces in the box. The preferred chemicals react to form gases as they polymerize and harden. The result is that the generated gases, when combined with the hardening action of the chemicals, forms a foam that expands into the empty spaces in the container and surrounds the object to be packaged in a custom manner. Typical precursors are those of the isocyanate variety that react to form polyurethanes while generating carbon dioxide and water vapor to produce the foaming action.
Although foam-in-place applications remain quite useful for custom packaging, they are somewhat disadvantageous in certain circumstances. For example, the foam precursors are typically injected from a hand-held dispenser or "injection cartridge" which must be operated manually. Additionally, the foaming chemicals tend to be sticky and find their way into many unintended locations during the packaging process. As a result, foam-in-place applications using manually operated injection systems remain an excellent option for packagers who need custom packaging on a time-to-time basis, but are somewhat inefficient for those requiring large volume packaging applications.
As a result, there has been developed a series of automated devices that produce plastic bags into which a foamable composition is injected as the bag is being formed. The bag can then be simply dropped into the box with the object to be packaged. As the precursor compositions form foam, the bag expands and surrounds the article in a custom manner. Such devices are described in U.S. Pat. Nos. 4,674,268; 4,800,708; 4,854,109; and 5,027,583; and in pending U.S. application Nos. 07,843,609 filed Feb. 23, 1992 to Sperry et al.; and 07/766,810 filed Sep. 26, 1991 to Sperry et al., all of which are assigned to the assignee of the present invention.
As will be noted from these patents and pending applications, the typical method of forming a foam-in-place cushion from a plastic bag is to heat seal sheets of plastic film material together both transversely and longitudinally as they are being fed from a stock supply to form a generally rectangular bag with the foam inside. In alternative embodiments, the stock supply of plastic film material can be fed in center folded fashion so that one side of the bag is a fold, rather than a heat seal. These devices have gained rapid and wide acceptance in the marketplace and have served their purposes well.
There are, however, situations for which heat sealing raises its own problems. For example, the task of heat sealing plastic requires a careful balance between supplying sufficient heat to seal the plastic while avoiding the amount of heat that would sever the plastic. In turn, this balance requires that heat sealing equipment will usually require adjustment to accommodate different thicknesses or gauges of plastic film material. Furthermore, in order to avoid severing, the heat seals that are formed may be somewhat weaker than would otherwise be desired. Additionally, plastic film material is often inconsistent in its supply characteristics so that even a sensitive heat seal adjustment may often fail to either completely seal the plastic or will entirely sever it. As another consideration, heat sealing tends to be more reliable for large volume, rapidly repetitive (i.e. continuous) cushion manufacturing, but is less reliable for the intermittent cushion bag formation that many packagers require or desire. Finally, heat sealing raises maintenance and reliability problems. For example, plastic material can quickly build up on a heating system after repeated use.
Therefore, the need exists for an automated method and apparatus for repetitively and rapidly producing foam-in-place cushions which minimize or avoid the problems of heat sealing.